Electeodepositiqn of metaiis



July 1 5, 1952 ER 2,603,593

Til. 2 l

July 15, 1952 P. s. BLlcKENsDr-:RFER 2,603,593

ELECTRODEPOSITION OF METALS Filed Jan. 8, 1946 4 Sheets-Sheet 2 July 15, 1952 P. s. BLICKENSDERFER 2,603,593

ELEcTRoDEPosITIoN oF METALs 4 Sheets-Sheet 3 Filed Jan. 8, 1946 Mm. Funai cunuu-r z IRo I l I l l I cunnzm' l l l l I l 30 HIN. I HR. I HR. 'I Nl- 4 NR. SHRSHIJHRQHR.

REVEISI m TIM! l ll tions.

Patented July 1/5 1'952 UNITED S'TATES aeoasse V i ELnornonErosrrioN or Philip. S; Blickensderfer, Hamilton, Qhio, assignori to i TheV Champion Paper and. Fibre Company, Hamilton, Ohio, atcorporation of 'Ohio i Application January 8, 1946,; Serial Nor' 639,813-

1 This inventon relates tothe'electrolytic deposition of metals andhas particular value inI-the local deposition of metals for the filling ofholes, pits, worn or peeled areas, cr-acks and scratches, the uniting of separate pieces, or forflother-purposes, and it has particular utility in securing and maintaining superior continuity and uniformity and a high degree of Vperfection in extensive smooth highly polished-solid or-plated metal surfaces.

IArticles'such as tools,--gages, etc., in which a steel--articlehas been proi/dved-with a wearing surface-'of -chromiunn frequently becomewor-n or damaged` in service sofithatl the chromium surfacing mustbe built up -or replaced. If-the plate has lbeen,w ornorhas -peeled off down to the base metal in even a small-part of the-platedlarea, or if it becomes so i'nA the preparation, Whether mechanical or eleotrolytic,-for repla-ting, it has heretofore been considered necessary Vto strip off all of; the chromium and=start afresh. `Solid or plated metallic surfaces of rotating drums, endless metal -belt,s; etc.V for use in the casti-ng'of lo'sic Vor'other films, oficoating on paper (as descrbed in Patent No. 1,719;166)`or the like, require a high degree ofperfection in-uniformity, smoothness, continuity, and freedom from cracka celluscratches, holes, Vpits or other d efects, so. that considerable 'difliculty-fhasl heretoforel beenexperience'dfi in Securing-the required degree Vof perfectio'nv throughout the-area of surfaces as large as-are-requi-red for commereial Casting opera- Rolled and-cast metals of 'the necessary surfacearea are all subject to the'presence -of vo'ids,r-.slagf-inclusions, and thelike, which --even vwhen--extrernely small are, unless cleaned-out,

filled to the edges, and polished over, sufiflcient to impair if not to completely destroy Vthe value of theisurface for casting. purposes. Eleotroplating, particularly` with chromium which otherwise is iahighlydesiralole material fora Casting surface,

ordinarily doesnot cover, vhut rather accentuates suchndefectsn the base metal, and alsofrequently exhibits other 'defectsfinot previously-apparent;` The. customary method.V ofstrip-pingloff all -Lof rthe chromum 1 and replating-whenever the base metal becomes exposedfiis-vconsequently -not -satisfactory for therpreparationtof such extensive surfaceswith'the required degree of'freedom ffromi even -minute defects, 'since the replating cannot be; dependedl uponV to reduce;` thel total number of such defects. Even Lwhen a satisfac- 'toryl surface rhas once ibeen-secured the problem :stillremains sincefin continued use-such surfaces are always subjectto-damage suchas scratches,

ficient to completely destroy the utflitywfacasting surface agfreatvmany squarev feet in area. Endless flexible belts, even if made of electro,- formedstrip arestll subject to objectionablejpinholes, etc. and areadditionally subject-in-service to suchfdamages as dents, teara and the lika. as well as requirine Splicine togive themtheir: endless form.

' The primaryiobject; of'the present invention-is to provide a method by' Whchholes, pits, cavities, dents.. Cracks, tearsrandflthelke. in;-m;eta1lio surfacescan be electrolrtical-ly filled, so thetefter sthepatches. are cut::down tofthe surfaoelevel.

for the.purposeofj'patching large: holes `(which may be due to cutting out damagedior defective portions) inthemetal belts or sheets lby.-;inse rtion of .a'- eopl-anar; inlay :of similar metallic: sheet lin tliehole andjeletrolytlcally. unitinglths -withthe surroundinggmetal torform' a. singlesubstantially nomogeneous sheet. Other objects and advantages-gof the invention-will:be =made apparentiby thefollowins description:

I have. now--fo1indl it possible, inraccordance rvazithf.l the present irwentionfl as hereinafter-fmore fully described, to successfully 1, accomplish't' the aforesaid. objects and fill leven" minute holes,1-pit's, scratcheslcracks, etc. in'a'ifinished solid'T oriplated metallic. surface,lso; thati al surface unfitilfor! use because -o 'such: defects. -can-bexendered smooth.

'substantially uniform. and. homogene'o'us, and

useful; for'itsintendedpurpose Byi-anianalogous method I: aansfill or. repairfiholes, cracks,V etc. which. extend?- throughf th'effthickness of metal belts for; sheets randjunite..clisc1`''ete pieces; whether for ipatching; holes; joining ends off'strips or? Hfor Idents,I nicks; etc.. one of'iwhicliisffrequently sufother purposes- I Ifihave-:i also -foundthat; by:` the methods :of -the 'present'ainvention as h'ereinaftr morejparticularliy described; I can repairi'orpatch surfaces:electroplatedwith-chromiumA even when worn; cut'orsetchedfthrough the-platefintofrrous baset: metal, so that; assumi'ng? the 11 surroun Vmg Vpor-mens;of:me original; plate tote properlyielarge extent are subject to defects such as-those 1 mentioned, surfaces plated withchromiumV are particularly subject to such defects, due to the well-known and characteristic difiiculties i, encountered in chromium plating. My invention, therefore, though applicable to the filling of defects in and with various metals, has one field "of particular utility inv connection with the filling with chromiumlof defects in a chromium plated "s'urface.

filling-of defects in a metallic surface is `accomplished according to the present inven- `vtion- -by first mechanically Shaping the defect,`if inot already of a form suitable for the electrolytic repairing operation, so that it forms a concavity or depression in the surface, the least 'width of whichis great in 'comparison to its depth. This concavity is made to present an `Jimbroken metallic, or A electrically conducting, surface `for the reception of a continuous layef 'of--the'metal to be deposited. If it'is undesir- 'ableto make the concavity as deep-asfthe defeet, the continuity of the electrically conductinglsurfac'e may be secured by using a closely ifltting metallicplug to fill the defect up to the Eleveloff the bottomof the concavity. In work- V'in'gi'on thin metalr (such as the metallic belts de- ;fscr'ibed in: PatentV -No. 1,'719,166), small holes Vmayl be plugged. as describedor, when larger areas are tobe filled, a metallic backing plate rmay-'sometimes-beL-used to give-the necessary 'as' nearly as possible identical conditions.

to flow through the cell, advantageously at a i rapid rate, washing over the surface of both continuity to thelconductin'g surface of vthe Vconfcavity,or an inlay ofsimilarthin metal -can be -fitted in thelhole' to reduce the area-to be'filled to'na' crack,-lwhich :is `then filled as hereinafter =more fully'describe'd'. 1 7

. This concavity is lthen. constituted one elec- :t'rodefinanelectrolytic cell or, if-formed in an 'extensive surface; is advantageously incorporat- Ied as onelwa-ll-'of-an electrolytic cell. of commen- -surate size. Its .1surfaceis 'then'l electrolytically tprepared byV appropriatemethodsl so that the subsequently deposited metal maybe firmly ad- :herent, after' which 'agplating' current'is passed through thecell. topthe 'metalsurface of the con- ;cavity'until the deposit has reached a thickness V 'adequate to-at least. zfill the depression `up to |the level cfwthehrequired surface. ..'In case of :thin belts or sheets of metal, if the exposed; plug ;J'S. obiectionable on the backof. the sheet,.a con- V ;cavity canbe formed around'the plug. on that :side of. the 3 sheet. also :and electrolyticallyfilled in: the manner described. I'nficase of a chro- ,.mi;um plated surface; which has been vworn, ;peeled,V cut, or etched :through to a ferrous base, lVor in which- ,the ;bottomoffthe concavity has been 1fj lled; with, an ,;iro n plug: of 1 material size, Iv Vflnd ;thatflinorderto secure satisfacto'ry. adherence of; thelelectrodeposited'metal, the current Vdensityufshould be,l controlled with 'reference to time, as-hereinafter fully set-forth. In ,patching me- -ltaljlic I surfaces,J as vdescribed, the conditionsofv disposition are in general imost' advantageously sefone form of fiuid circulating system for mainanede and cathode. After the required thickness of metal has been deposited, the cell is dismantled 'and the excess metal is mechanically removed down to the desired surface level.

The process and apparatus used will be more fully described by reference to the accompanying drawings, in which:

Fig.; 1 is a. schematic and greatlyenlarged cross section through a defect in a plated metal surface.

Fig. 2 is a similar cross section through a defect showing where additional metal isdeposited when attempting to fill or cover such defect by the customary plating procedure.

Fig. 3 is a section of a similar defect after mechanical 'Shaping in preparation for local' plating, showing the anode in position.

Fig. 4 is a similar section of a defectpreparedv I :defect in a fiat surface.

, Figs.V 8 and 9 are two views-of a modified vforrh of cell usedffor filling elongatedrcavities such v as cracks or scratches.

, Fig. 10 is a typical wiring diagram for the apparatus used. 1

Fig. 11 is a diagram showing the current densities used plotted against time, fora typical defect filling operation on chromium plate. Figure 12- is a diagrammatic representation of taining a flow of electrolytic solution through the `plfitins cell-V V i.

Fig. 13 is a `fragmentary cross section'of a metal sheet or'belt at an opening whichextends therethrough. A g

Fig. 14*is=a section of the same after a depression has been cut extending in` opposite directions from the opening and the opening? itself has -been filled with electrically conducting 'material flush withz-the bottom of the depression.

Fig..15 is a section of -the same after the eleclytic filling of the depression.

;cut on the oppositeside. .,-;Fig-. 17 is asectionfof the same' Fig. 16 is asection of :the same after the sheet hasV beenturned over and af depression has been afteruelectrol-lyticallyfilling the second depression. s Fig. 18 is a section of the same after dressing faces'of the sheet.

down.: the -fdeposits tolevelof the adjacent'sur- V Ffig. -19 isia sectionV similar to Fig. 14 butshowp i with the surface of the sheet with no depression. I; ;Fig;v;2(l is a crosssecticn-of the parts shownin When'the `defect is 'the preceding figureafter -the-eleotijedepcsition Fig. 21 ^`fsfasectionof the same after -thel sheet hasberen -turned over and va depression Vhasibeen ctli'n the oppositesicle.

theoppositesideand. elctrolytically :filling itwith metal.

Because of its especial utility in connection with the filling of v defects inchromium plate, the invention will now 'be described'asembodied in a process and apparatus particularly adapted to thisuse.V

Referring to Figs. 1 to 6 of thedrawings, the basis metal 21 isshown covered by a. layer 22 of chromium in which there is a defect 23 in the form of apit or crevice which vmay besupposed to rhavehad its Origin in a microscopic defect, pit, Scratch, or bit of slag, etc. 24 in the basis metal 2I'.4 Any attempt to fill or cover this defect by 'further deposition of chromiumin the usual manner,v results inthe preferential deposit of metal 2.5 at the edges 26 of the defect, which simply serves. to accei tuate rather than cure the defect. V;Inv order to make possible the deposition of metaltofill the defect solidly to the bottom, I first grind or polish out the' defect until solid 'nietalis reached, cutting into the basis or backing "metal if 7necessavryand giving the defect the form of'a concavityfl (Fig. 3) whose width is materiallygreater than itsdepth.v In order to further hinder the preferentialdeposit of metal at the edges of the depression, these edges may 'beigilven a gently rounded contour as shown at Bi in the figure. Above this is located the anode `33 which. is advantageously roundedto. a radius 'ofurvature materially smaller than that of'the depression 30 and'is located aproximately centrallythereoverand closer thereto. than the difvference between the respective jradii, so that the anede 33 iscloser to the bottomof the concavity V311thanto its edges 31. Although this spacing is' desirable it may be departed from to some extent, particularly When electrodepositing some metals With a betterthrowng power than chromium. 4I-Iovv'rever, it is not recommended that the distance from the anode to the center of the concavity ever be. relatively very much greater than the distanoe'from the anode to the edges of the oonoavity. By the means described-I find'itpos- 's ible to so control the rate of deposit that, even withjchromium, the center of the concavity is filled without undue building up of thedeposit around the-edges. This is believed to result ffrom 'aihfig-her density of the plating current atV the enter, due to the Shorter distance from the 'anderand to the absence of-urrent concen- Vtration:aroundr the edges. dueito--their-greater distance from the anode anditoV the -rounded Contour given to them.

I A i U h 4 deep, the operation-ofcuttirs ett the. .eefet as ulv-strand `i.n' ,1fig,. 1.3 may ;the: deposited metal. :Copper require-a inge-amountoffl cum-ng andefiieseessivelyflo'ng-plating" timei for filling. In' suchficases, inorderV tosecure a continuous electrically -conducting base' for-thedeposition of ;a continuous layer'of electrolytic metal,v it is ;frequently-fadvantageousito jfill iin ;the rbottom of 4the-'defect i and hollow out only nthe' part near-the ;surface as shown inLE'ig. 4 ratherl than to-cu-t down -to-'solid -metal as in Eig; :3.

defect to fit the plug; asindicatedinJFig. 4; Otherwisethe--plue mayibefitted into the defeflt as injdbal-3edV in Figsf and 6, Theplug usedfshould becarefullyand securely driven'into place sothat no'openings are jleftbetween it''andgthe surfounding metal. The nroportionpf the? depth which nay be'fiued meehanicauy and that which must'be cut down depends on the 'widthnoffthe detect and thetype of fillng used. Withrfillin'gs having littlefineehafnical strength; suehf. as lead, the :depth of the depression3fi'isadya i geo'usly as much ;as three times 'thewidth of'jt 'top of fiuing et. on the other hand,iwitusimnger fillings.. such as iron,;the depth of theidepression 3.0 may sometimes safely bevv as little as-thewidth of the topof filling, 35. 'The interior kofjtlqie. concavity should then be smo'othed Land cleaned,` and the edges V;-H rounfdedoif as' for the purpose described.

the concavity-should becarriedIo-utwith great f r-I`his'flsrnoothing' and cleaning of'fth'e 'interior of care. inorder 'to provide the'eoncavityiwithffi a smooth, '..contnuous uninterruptd electrieally conducting. siirface:'thi'toughout4 its ent e.- Anyliabrupt change fin Vslop'ellqr; in surfja'e. any point ihth. i be 'completely polish'ed out.. .."Any. surfaeefiidiscontihuities lsuch Ias minute Vfor l'fier) fcrac cre'vices, or even slight differencesfliri surfav vel,

. msi-the .=.0.nnd the adjacent menter-at any other part of the concavity, should beficarefully. eliminated- Any dirt sreasameiallic 9.. idesorother deposits which might interfere with; lie-uniform electrical conductivity of the surface of the-dapression should ;he `completely removed theref- -With'theflanode;.g33 located as described and as illustrated V inA Figs. 3 and 4, both the Y anode between the filling-in the, bott 3 3 jand the concavity Maresubmergedin a usual type -of chromium lplating bath whichI advantageously allowed to contact the .original;-..chr.o-

miumV surface for only a relativelyN short 'distance beyond the edges V3 I of ;the..concavity :311.-r 'f I; find that the successful filling'of theiconcavity is much more certain, i the deposited. fmetalzmore sound; and the time required to filltheconcavity is: greauy. reduced iffthe min Lisskept 'ineapid :motion `past both' anode and cathode :fc'oncavity f .30) JAWhile theplating: is infV progress::=1!I=hisemay- ;aeoasos solution from a supply reservoir and passing a rapidly fiowing stream over and between the electrodes and thence returning the solution to the reservoir for reuse. The fiuid velocity through the plating cell should be high enough to give turbulent flow through the cell. Higher velocities have ordinarily been found to make possible higher current densities and higher rates of deposit and thusshorten the timerequired for filling a given size of cavity with a given metal. Suitable velocities'depend on the metal being deposited, the type and temperature of the solution used, the current densities and plating rates, etc. For filling concavities of the order of 1A; inch in width in chromium with electrolytically deposited chromium, I find a fluid velocity of the order of feet per second to be satisfactory, though with other metals, such as nickel, ma-

terially lower velocities maybe used. These high velociti'es make possible the use of current densities much higher and rates of chromium deposit'much more rapid than are otherwise attainable.

The temperature of the bath and electrodes may be vchosen from a wide range as is well known in the art. Because of the known fact that higher current densities' and consequent higher rates of Ideposition are possible at higher'temperatures,

'the use of such temperatures is often advantageous. When, on the other hand, as is often ad- 4vant'ageous for reasons hereinafter explained,

subatmospheric pressure is maintained in the plating cell, temperatures high enough to cause 'boiling or cavitation in the cell or other parts of the circulating system should be avoided. The temperature once selected should be maintained within rather close limits during the plating op- 'eration, as is well understood in the art.

Even though the concavity to be filled has been thoroughly cleaned mechanically and by wash- Ving with solvents to remove grease, etc., I findV 'that an electrolytic "preparation operation is ordinarily advisable to insure a satisfactorily adherent deposit. For this purpose I prefer in the case of chromium to start the operation with a` reversef current, temporarily making the surface to be plated the anode. As is Well understood, care should be taken to avoid lexcessive strength :orgduration of thisreverse current to avoid'unnecessary' eating Vaway of the metal;

f After'this anodic preparation, the. surface to 'be plated'is made cathode by reversing the direction of thecurrent. Under the conditions described, vthisrv change is advantageously made quickly since I have frequently observed poor adhesion of the-deposit in cases where much more than one second Was allowed to elapse during 'this reversal of the current.

I have -now made the '-furtherdiscovery that `a highv quality adherent deposit of chromium can be secured, even when the steel base metal is exposed through, or adjacent to, the original chroplate.l- This can rybe' accomplished; I find, by, immediately following -the 'anodic preparation Vof. the :'surface; with: current ofV somewhat less than minimum platinglde'nsity passedthrog h the-chromiumfplatinglsolutionto the surface of the depression asf cathodeV for? at:v least: af short time before increasing the current density to al valueV atflwhich deposition of chromium takes place. As :is w'ellV known vin fthe chromium' plat- -ingfart, 'noi' matter what the. applied fvoltage, no imetal `|vlillfbei`t1e'posited onlan'y part of the'cathode I ;where the ;current fdensity; belowl'ar minimum valueV F whichr-is fdependent. Von the temperature,

4 minutes.

composition. and proportions of the` bath, etc.. but is fixed for each specific set of conditions and -canbe readily determined by routine tests.. If

temperature, and other operating conditions the.

required duration of the less-than-plating-density current can be readily determined by trial.

In some cases only a few seconds may be required whereas in other cases 30 to 60 minutes or more may be desirable, as no harm appears to result if the time is extended beyond the'minimum requirement. i

After the current of less than minimum plating density has been passed for the required time, as described, the current density is fincreased to the working value. As hereinbefore stated, runiformity of the patched surface 'is most conveniently secured by substantially duplicating |the current density and other conditions used in Vdepositing the original plate. With this limitation the working value 'of the current density is advantageously as near as possibleto the maximum at which an unburned deposit is vsecured, as the plating'time is thereby reduced.

When the desired depth of deposit is secured,

the plating is discontinued and the plating" bath,

the anode and all connections are removed as hereinafter more particularly described, leaving the patchv as illustrated in Fig. 5. The surface is then cleaned and the excess of deposited'metal mechanically cut down to the level of the surrounding surface and finished 'as desired, lleaving a smooth continuous surface at the'original rsurface level, as illustrated in Figt. 6.

The described changes in current direction and density, with time, are graphically illustrated in Fig. 11 which shows the values of cur- 'rent direction and density, plotted againsttime, in a typical defect-fllling operation on. kchromiumplate at a temperature of'? F.

Referring to' Fig. ll it will be seen that-a Vcurrent of approximately the minimum plating density is allowed to 'pass in rever'se direction for about one minute,V that the direction is vthen quickly changed and a current of density'sligh'tly below the minimum plating density is passed in the normal direction for approximately 20 The density is then increased to an effective. plating value. I have found that when this increase is made gradually in the normal manner as 'shown by curve A, the deposit is-satisfactorily adherent, but when the excessdeposit is polished ofi', a ring of what appears to Ibemmetal of a different structure 'is evident around the edge of the defect. I have further found'that if the increase to maximum current density is made quickly,.as indicated by 'curve 'B, this` ring structure is absent and the deposited'metal appears to be homogeneous Vand integral with the original chromium. Then when 'the excess metal deposited has been polished off,H it is found'to leave a surface on whichith'e old and new -metal appear to be uniform vin smoothness and structure. Alternatively, in

some cases, the re'verse current may be followed directly by current of plating density'as indicatedby curve C, though I prefer -to use the current densities; indicated by curves- A, or B, as described, inf-'orderto insuremore perfect adhesion. f f

Since the conditions under which the original plate was deposited maynot be known, it may notbe possible to duplicate them exactly in making-the local deposit, which. may therefore differ slightly from the original plate inV some little understood manner; As a result; the'local deposit when polished' oifto the' level of the originall metal mayV reflect light in a,r slightly different manner, thus appearing, when viewed fromsome angles',-as a spot on the surface; but forall practical purposes the Aold and new'metal appear to be integral'andhomogeneous. I'Iheapparatus of the present. invention used in carrying out the process describedncan 'be varied to suit the conditions.. Fig. '7 showsin cross section one form of apparatus found Well -suited for use in filling smallfcircular or ynearly circularl depressions in chromiumplate.,-- Referring to 'this figure, which isdrawn toa' much smaller vscale than Figs. fl 'to :6, the lchromi-um i plate 22 is shown as a single line onfithe surface of thef'fbase. metal 2I. rfhe anode33 is, supported centrally 'over the polished-out conoavity- 30 ;by meansof a cell body 40. This maybe composedfof a non-conducting rsubstance such. as glass or 'at Synthetic resin ..which is Vnot attached Vby the' chromic acidr bath,-.orf it -may be composedof. a nonfi-reactive metal suchas lead, if provisions :are made to insulate it electrically from' 'the surface. 22 and; from 'the anede 33. washerzfll vis used to preventjeakagebetween cell "body. 110 and surface 22.. This'washer Vmay advantageously" be made of a synthetic rubberlikecomposition Vwhich is not affected by the chro'mic acid, 'is' a good di'-electri.c,'and possesses suffi-cientplasticity' to form a good seal.V I have found SyntheticV rubber-like compounds of the polyvinyl chloride type well Suitedr to this purpose'.` The washer 4! is cut out to form part of'the walls 'of the electrolytic 'cell 42'. It serves to'insulate the body 49 (ifmade'of metal) 'from the' metal cathode surface 22, to prevent in'.- ward'ileakage of air (whenthe systemf is maintainedw'at 'subatmospheri'c pressure), to prevent outward leakage of fiuid, and'to preventcontact of the bath with the "surface122f beyond the area' 'on which a :deposit is desired. To assist in'. the last-namedffunction, the surface-of; the metallflf-where a. deposit iisl. not wanted: and thatof washerV 4| may be `Vpainted with a stop off compound of known -type before the apparatusis assembled.

' The anode'i33i extends into the. cell S42' through all-'opening 4'3 in: body 40.. If-body=4iliis made ofl metal vorV of a non-yielding. s-ubstance such as glass, apositiveiclearance Vis usually' -necessary at thisxpoint. The. anodeiis held in placerand sealed agains'tfleakage of air-'orbf electrolytelr by ,a' rub,- ber :packing'lh which may be protected from the chromic'facid by-a'washer 45 which'may be made ofthe :same acid :resistant material as washer.4 l

The'arrode 33 ..m'ay be made of any material. customarily used'for anodes in 'chromium' plating, I fin'dglea'dt wellsuitedto the purpose; It extends through 1the:rubberpacking ringf44- and may be provided-with ahandle 4.6, which may be'of a more-:rigid metal, by lwhich the distance of the anode=:33-from-the coneavity 3iljmayfbe adjusted by hand. ;The necessary electricconnection may be made" holland-lede by a suitable clamp 41 and wire- 38, leadingito a -suitablefseurce of current 49; The cell may be held in place on surface 22 by (means of a pressure'block 50 and screw 5l which may be held in-a member52 which, may be any part that is or may be fixed withrreference to the surface 22.

The electrolytic cell -42 is provided with anim let conduit 55 and an loutlet conduit 56 through which a continuous fiow of theelectrolytic solution may be passed into and outof. the cell 42. The cell 42 itselfis advantageo-usly ofismallflvol; ume so- 4that -high -fluid velocity 'may ;be' main,- tained therein. The conduits E55 andv 56.. are. ads vantageouslyeV pointed directly at anodehSB :and cathodetlsothatthe stream of liquid continue; ously washes the surfaces of both. electrode's...4 The abruptv changein direction of flowiillustrat; this ';figure is also of advantage in as-Sfulrjng turbulenceoffiowin the cell42. i j 11,;

Eorl filling elongateddefects such as cracks and scratches'a modified type of cellV such as that illustrated in Figs. 23 and. 9. may be used. v '.l'hese figures arelongitudinal and' transverse. sectional views respectively. of ;one formof lapparatus rused for this.. purpose.. (They show ...the'v apparatus clampefd. onto the 4 same. chromium plated surface 22of.base or. -backing metal 21., Theconcayity |30`is theresult of cutting out a crack or scratch in the manner described, so that itswidth isjgreatv inproportionto its depth and the edges advanitageously have' rounded form. The 'anode: |'3,3, is elongatedin form to correspond with the concavity (3.0.. The body Oofthe cellisof a cor-. respondinglyelonga'ted form Both anoder 13.3 and .-c`el1 body 140 are, in this case, advanta-- geflusly, made -of lead which. permits ythernftci' be bentl to.conform to-thecurvature of any. cracl; ;or Scratch which may require filling, V''I'he cellbody I40 asybefore, sealed' againstand insulated from surface 22 by a Synthetic rubber-flise washer IM which is cutout'to' form -a part of the waus of cent M2.. The opening 1.4.3 Withithe rubber packing 144 and 'synthetic rulcvaber-lile| washer M5 permit T-shaped handles M5. to'enter the cell andgrip. the electrode '133, whereby'the distance betweenlanode 133 andf'cathode 13g can be adjusted as and4 for. the purpose previously described.. `The.. solution of electrolyteffiows through 'the cell :from inlet` |55 to-Ljoutlet 15,6; A clamp 4.1. serves as before p i to wire 48 leading toa suitable source of current 419.| The. cell is held injplac'e aslwa'sjcell "Npy meansof apressure block Illandnscrew Vlil/in member. 152 which may beahy'partsuitamyfixeq I withreference' to surface 22.

The chromic acid lating bathsused are not only highly corrosiveto hands and clothing' -o f OPratorsbut even i V metallic. chromium plate. Itis therefore :highly desirable :toprevent leali'agejo'f the'solutien from the een ancother nartslof the apparatgsasweu; This' is most'readfly anaieffsiirely aeeqmpiisheg by maini'ai'n'i'rig .-subatmosph.er1c..pressurefwithie the' cell: and'. all' parts' of' the circulating sys`,tem subject to leakage; so; that the circulation through these. parts of: the. system is' maintainedpby 'sucfd Y tion' rather. than positive. Pressure.. It is ordinarilyalso. advantageous to' maintain thefsurfaee being platedfii'n avertical "or an invertedposition.

- IThe circulatin'g systemfiitslelf' dDes nOt Qifm Slag partV of the present invention and any suitable type may be used.: One. type whichis adaptedgto the. simultaneous filling. of a considerablelnumber of defects isillustratedin Fig. 1 2-n..w-hch ajanl; 6dis provided for storageo-f the...plati'r;g bath,

tankr should be lmadelc'if.material, w,l'1' J h" to'ponn't, the anede damage the surface. of' jthe 1'1 be substantially unaffected by and will not sig-1 nificantly affect the composition of the plating bath. 'I find a high silicon acid and corrosion-f resistant iron suitable for the tank and for other parts in contactwith a chromic acid bath of the sulphate type. This tank is provided with va vent BI to atmosphere. Thefiplating bath is circulated by a suitable pump 62 which delivers fluid through pipe 63 into VtankV 00.v Bysuction thepump 62 draws fluid from tank 60 through conduit 64 to header`65 from which individual tubes 66 lead to each of a pluralityof cells 40 and/or M0. The

' fluid after i'passingthrough the cells 40 passes throughltubes 61 and is vadvantageously discharged through. nozzles 68 into. glass 'chamber 60 from which it flows through pipe. and` valve 1'I tothe pump 02 which returns' it to tankf60 as described. The tubes 66,161 are advantageously madeof a' syntheticlrubber-like compoundv of a type such as that already described. The glass chamber 69 is provided so that watch may be.

kept on the fiow through each individual cell to assure satisfactory results in each. 1 A valve 12 may-be provided -for draining 'the'tank when' desired.. It will be apparent that the pressure in the 'entire system from conduit 64 through the cellsl 40 tothe'pump 62is subatmospheric. Any leakage will therefore be inward leakage of air and not outward leakage of the chrcmic acid bath. Damageto the surrounding. chromium plate and injury to theperson or clothing of the operators is thereby avoided. In usingfthis apparatus, when the plating is completed (as determined from av knowledge'ofthe depthof the depressions to be filled and the current densities used and resulting ratefof deposit), ventvalve13 on headertr is opened thus breakinglthe vacuum in the system and ,allowing the individual plating cells to be sucked dry. In cases where only onev cellr isdesired tobe shut-downlat a time, this is done by clamping shut the inlet tube 66 leading to the cel1`,.then slightly loosening the cell from the surfacel 22, allowing air to leak in. As soonas the cell and outlet tube 61 are sucked dry the outlet tube is also clamped shut. The system as a whole Jcan then continue' to function with the remaining cells still-in operation. Also acoil 15 maybe provided in tank60 for' controlling the temperature ofthebath in aknown manner.

=Fig 310 shows the electrical connections used. The cell representedby. anode 33 and cathode`30 cut in-the surface 22 is supplied with current from any suitable source such as battery. 49, the

positive pole-of which is connected through adjustableresistance-Bl, ammeter 82 and reversing switch 03 to anode 33.' The cathode30 is con nected through switch 83 to the negative pole of the battery. In starting,V the switch 83V is reversed for fal short time, as. described, making 30 the anodeand 33 the cathode, butswitch 83is soon thrown to the normal position shownin thefigure. Whenalpluralityof cells are used simultaneously, as described, a separate circuit can be provided for. each, or allcan .be supplied from a single source, of current, asJwill be well understood by those skilled -in the art. VI prefer, however, to supply each cellwith its own ammeter V132, and adjustable resistance 8l., so that the individual current densities can be controlled to appropriate values.,. i i

'The invention as so far described is embodied in a, method of filling defects in the surface of thick metalgsuch 'thatonly one surface thereof required consideration. This is however not always the case, particularly in the case of metal sheets or castingfbelts to which reference has already been made, and the invention'willL-now be described as embodied'in a methodof closing small or narrow holes or openings which extend through the thickness of such sheets or belts..`-

' Fig; '-13 shows a cross section through a' metal sheet 20! exposing an opening 202 extending through the sheet. This may be polished outto form a depression or concavity 203, and thehole of deposition, will be adapted to the particular metal being used infac'cordance with knownprinciples. f Thev high 'velocity of the electrolyte through 'the cell -is usually unnecessary in such cases andif' the cell is of considerable size, even the circulation may not'b'e required. f After dep-' osition the'part appears asfshown in Flg. '151.' If the exposed filling 204 is 'objectionable on. the reverse'side of the sheet, the sheet is turned over and the 'filling 204 is preferably, though. not al- Y ways necessarily cbmpletelylcutout'to form a new depression 201 substantially opposite to the filled depression as shown 'in Fig. 16.;'The smooth un-L interrupted electrically. conducting; surface 'of de pres'sion`201' is'foi'med' partly of :the metal of the sheet 20l'and partlyfof` the' electrolyticallydeposited metal 206'. This isfp'repared'forthefre ception of an adherent deposit and electrolytically filled with repair metal 208 in the manner already described. It then appears asillustrated in Fig. 17. iIf smooth surfaces are desired on each side. the projectmg parts of the deposits 206 and 200 may be mechanically dressed down to the planes of the adjacent surfaces, though the dressing down of the first deposit 206'may frequently be more desirably accomplished prior to the cutting 1 of the'dep'ression 201 on the oppositeside.

is the same as the`electroplate, while thev depres-i sion on` theother side is-'- advantageou'sly Vfilled with metal which is the same'fas 'that formin'g the body of the sheet. In the case of sheets/composed of a single metalthroughout their-thick-I ness, the first side operated upon needlhave no more depression than is inevitably 'formedfby the mechanical and/or electrolytic preparatln for reception of an adherent electrode'posit. 'This V extreme difference between the depressions'on the two sides is illustrated in Flgs.. 19 to 22; lnclui. sive. A In this case the opening insheet metal4 2H is filled with electrically conducting materlali-at 2 ll fiush with 'the upper surface of the sheet. limited area of the surface surrounding theflll'-' ing material 2|4 is blocked off by stop ofl' 'var-v nish 2|5 or the like as' shown lin Fig. 19,`andls prepared for the reception of the required elec-' 1-'31 trodeposit. Metal 2 |6 is electrodeposited` over this limited varea as shownin FigfZO. ThesheetV isthen turned over and the 'filling material and adjacentmetal of the sheet is mechanically cut outV to form a. depression 217` which cutscom'- pletely through the sheet into the electrodeposit 2I', completelyremoving the filling material 214 (see Fig. 21). IIhis depression then has a smooth, continuous; uninterrupted electrically conducting surface: and is electrolytically filled with metal 2|8 as' in the previously described embodiment and illustrated in Fig. 22. The: surplus metal can thenibe mechanically removed, if desired; 'to the level of' thev adjacent surfaces as indicated by the broken lines in the figure.

.It can be seen from Fig's. 13 to 22 thatfthe process of closing openings inrsheetmetal: can beused: without essential change regardless Vof whether' the opening isya round. holeor: an elongatedicracktor slot or the opening. between abut'- ted'edges of discrete sheets orrparts. If Vthe process is. used to electrolytically' join..the 'sides of 2' long: tears er slits or.: the edges 'of discrete sheetshitzis desirable to solder or cement the metal-f adjacent the abutted edges 221, 222 tora more rigid block or bar-'223'Yas illustrated' in Fig.

232 P'The process is then carried out as described with'referenceto Figs. 13 to 18 or. Figs. 19 to 22, asfdesired. J

Thismethod of uniting discrete parts mayr be used:` to...un'ite the ends of strips. to form'endle'ssbel'ts. butfit' has aparticular utilityV inpatching largeuholes in metal beltsor sheets, fas shown in Fie'.` 24.' The sheet.l 23I1has' alarge hole into which apatch' 'or inlayV 232 ofthe samev material andixthickn'ess 'is fitted. Both are soldered'or' cementeditoasuitably rigidblock or bar 2-33, to

holdithemrfirmly in the same plane while'the 1 opening.. between them is beingV filled With solder Or'other'electri'CaIly conducting'material 234; and until4 they arerigidly united by the first electrodeposit 2'35 asfin Fig. 15 or Fig. 20. If the sheet 231 sfinotl then suffici'entlyrigid to permit satisfactory handling in the' further steps of the process the other side may be mounted on a relatively rigidv block or bar 236 withsuitablespacers 231r interposed` as shown in Fig. 25. VWhile so mounted the depression on the second side is cut out and electrolytically filled; and. if desired, dressedwdown to the level of the surface of the' sheet asalready described.

The application of the process willbebetter .und'ersto'odi from'the following examples; the.

first; six ofl which| illu'strate its use'in the successful filling'fof Vcavities inv chomium plate whilev the last two illustrate its use inpatching 'of Nthin sheets or'belts of nickel:

I Eample 1 I 1. Composition of plating bath-Chromi'c acid 250' g.. per liter; boric acid 30 g. per' liter; sulphate ions=1/1to of 'hexivalent' chromiu'm ions.: 2. Temperature of bath' 160 F. 3..Diameter of concavity to be fil1ed'0L062 inch. 4. Depth of concavity 0.0015 inch. 5. Filling. in base of defectf'i-iron. 6.V Distancebetween electrodes 1/8 inch; I 7'I1C'urrent densities-Reverse 38.2 amperes per' square foot'for 1 minute, quickly changedfto 'direct 39.8 amperes per square foot for approximately 1/2 hour, then gradually i'ncreased over about LiOrninutesto direct V540 amper-esper square foot for 1% hours; 8'. Total time 2%; hours.

severe-N Example 2 Same as Example 1 except that increase from 39.8 amperes per' square foot to 549'amperes per square foot was made quickly (as rapidly 'as'i i rheostat could be set) instead' ofover a period' of 40 minutes. Results the same except that no ring structure was visible. i

i Example 3 Compositionof plating bath same'as in Exam'- 'plel except that' sulphate ions-:l/go ofl heX- va'lent chromium ions.

.' Temperature of'plating bath 160 F.

`. Diameter of'concavity to be filled 0.15 inch.

. Depth of concavity to 'be fi1led70-007 inch. 1

Filling in base of defect-lead.

; Distance between electrodes 1/8 inch.

.^ Current densities'f-reverse 19.7 amperesl perv square'foot for 1 minute, quickly changedtoV direct' 19Iamperesper rsquare foot for '1/2 hour; increased over a period of about 40 minutes'to direct` 400 amperes per square foot for' 7 1A. hours.

'.' Toital time'7% hours.

. 'Results-good adh'erent plate; Ringvisible as in'EXamplejl, but no other evidence of lack' of' homogeneity.

. Example' 4 p V Composition' of plating bath-same:| as 'in-:Exe-

arnple3.

2r Temperature'of plating bath 160. Fr r Concavity (Scratch) width'lle' inch, lengthv 11/21' inch.. :f

. Depth of concavity"0.0905 to 0:0015 inch.

; Fillinglnot needed.

. Distance between electrodes'l/g inch.

'. Current densities'sa'me as Exam'ple 1 except plating current on for'21/2 hours. i

'. Total time 3 hours. l I Results good adherentplate. Ring visible'but apparently of n'olpractical.significance.

(OCO 4103019 Eample 5 Composition of pl'ating bath Vsame as in rample 3;

.' Temperature' of plating bath 164? F;

1 Concavitydiameter 1.11; inch;

` Concavity-depth 0.003 inch.=

AVliiillinglnot needed.

. Distancev between electrod'es 1A; inch.

. Current'densities same as Example 1 except' plating current 523:.amperes per square'ifoot for Lll/z'vhours.v

i Totaltime 5 hours. i

. Results same as Example 1.

per square foot for 2; minutes, quickly changed toforwardcurrent 30 amperes per'square foot 'for 1- minute, quickly increased to' forward cur- 4 rent 2000 -amperes per square foot for'57 minsa V Current densities--reversecurrent arnp'eresl acids.

8; 'Total time. 1 hour.`

9. The deposit was tightly adherent, bright, and

This example involved the patching of a pini hole extending through a hard electroformed' sheet of nickel approximately 0.010 inch in thickness. The hole was filled with solder and, with a small hand grinder, a saucer shaper depression was hollowed out around the filled hole as shown in Fig. 14, the solder filling being flush with the bottom of the depression. In the filling operation care was taken to avoid flux pockets particularly between the solder filling and the sides of the hole and to limit the area and degree of heating toprevent distortion of thesheet. The surface of the nickel in the depression surrounding the solder filling was first scraped as free as possible of excess solder and was. further polished using sandpaper of i increasing fineness. polishing of the nickel surface of the depression wascompleted by use of a paste of diatomaceous earth VandWater and clean cloth. The surface Was then electrolytically prepared for reception 'of an adherent electrodepositby anodic treatment in a strong solution of sulfuric and `phosphoric Because of the large extent of the surface of thesheet'thistreatment and the subsequent electrodeposition were carried out in a small cell set up and clampedin place, with an interposed rubber gasket or the like, on the sheet metalsurface and including 'the depression and immediately surrounding surface. After'the anodic treatment the cell and surface were thoroughly rinsed withwaten The plating current vwas then started simultaneously with the introduction of the nickel plating solution into the cell, care being taken in the process to avoid excessively high current 'density on'any part of the surface. After the lowest part of thedeposit had reached the level of the adjacentisurface of the sheet as shown in Fig. 15 the operation Was stopped, the solution removed from the cell and the cell removed from the sheet. The protruding parts of the deposit were dressed down to the level of the surrounding surface and the sheet turnedV over. The hand grinder was then used to form a depression opposite the filled depression, removing all of the solder filling' 204 (Figs. 15 and'1,6). The'newly formed depression had a continuous smooth nickel surface throughout its extent, composed 'partly of the nickel of the sheet and partly of the nickel electrodeposit. This depression was then polished, prepared, and filled with nickel in the' same manner as was that on the flrst side. The surplus electrodeposited metal was then mechanically dressed down, giving the patch the same thickness as the sheet itself. The patched sheet was then substantially uniform and homogeneous, and whenV given the desired surface finish, was suitable for use as a casting surface for films or coating on paper.

, Example 8 This example involved the repair of a damaged and punctured portion of a large electroformed sheet of hard nickel approximately 0.015inch in thickness. made by a'blunt object which stretched and distorted the metal surrounding the puncture itself,

The i Thepuncture appeared to have been strength and hardness established'for the sheetr i' the level of the surface of the sheet.

sheet was-then of substantially uniform thickness and substantially homogeneous throughout, the V dis'tortedV area by a circle cutter, Tin' a manner to :i

cause no further distortion. This resulted in a circular hole approximately two inches in diam-4 et'er in a flatnickel sheet.

A two inch circle of nickel was cut from a sheet of the same character and thickness and fitted into this hole. 'Both' pieces were then cemented in a coplanar position on a heavy block of steel asl illustrated in Fig. 24'. In order to prevent further distortion of the metal this cementing operation was accomplished with' a commercial thermoplastic cement softening at about C. The crack between the patch and the sheet Was filled with solder as at 234 taking' care to avoid fiux inclusions and overheatingof the metal. The central partV of the patch and the surface of the sheet surrounding the hole were painted with stop off varnish, as at 2|5 Fig. 24,'

leaving an exposed annular surface of metal extending for a short distance on each side of the solder ring. This annular area was polished and electrolytically prepared anda layer 235 of nickelof about 0.020 inch thickness was deposited there-V on, in the manner described in the previousex'a ample. The solution and cell were removed and the now united parts were removed from the backing plate by softeningthe thermoplastic cement. The sheet was then turned over and cemented to the flat surface of`a backing plate 236, as indicated in Fig. 25, with interposed spacers 231 to provideroomfor the electrodeposited ring 235, which -was smoothed down on the level of the' surface of thespacers before cementing to the backing plate; Thereafter the solder was mechanical-f ly rcutoutto forman annular depression as indi-' cated in Fig.72 l. The surfaces were painted with stop jolfvarnish as, before, the annular surfacei'of the depression was polished and prepared, and

nickel was electrodeposited therein from a' solution' and underconditions as nearly as'possible duplicating those used in the electroformation` of the sheet. Before removal of the sheet from the backing plate and while the sheet wasv still,

held firmly in a plane position the electrode-` posited ring was dressed down to the level of thev surrounding surface. The backing plate was then removed by heating to about 100 C. to soften the cement used, and the newly finished surface; was cemented to the plane surface of a similar backi'ng plate to' hold the belt firmly while the initial annular, deposit 235 was dressed down tov The patched-V surface was uniformly smooth, and no evidence of the patch was apparent. Tests indicated that itself. 1

In the case of a chromium plated surface where there has been local peeling oif of theplate, a,

satisfactory repair may be made if the surrounding portions of the plate are adequately adherent to the base metal, by polishing out the peeled area, rounding off the edges of the surrounding plate, and then completing the repair as described.

In the case of worn chromium plated gages'and other tools, the natural Wear is frequently found i to have given the worn area theform of a wide' Vis) lic chromium, a defect in a chromium plated 'surface, which comprises: mechanically cutting out the defect to form a depression whose least width is great compared to its depth; filling any part of the defect which is deeper than said depression, with electrically conducting material; providing said depression with a continuous uninterrupted V electrically conducting surface throughout its entire area; constituting said area one Wall of an electrolytic cell; electrolyticallyr preparing the surface of said depression for receiving an adherent electroplate; thereafter passducting surface throughout its entire area; blocksolution through said cell, submerging and Washing an electric current through said cell to the electrically conducting surface of said depression, as cathode; and maintaining, during the passage of said current, a substantially continuous flow of chromium plating solution through said cell,

submerging and Washing over the surface of said depression. i 5. Process of electrolytically filling, With metallic chromium, a defect in a chromium plated surface, which comprises: mechanically cutting out the defect to form a depression whose least Width vis great compared to its depth; filling any part of the defect which is deeper than said depression, With electrically conducting material; giving the edges of said depression a Well rounded form; 'providing said depression with a continuous uninterrupted electrically conducting surface throughout its entire area; constituting said area 'one Wall of an electrolytic cell; passing a rapidly flowing stream of a chromium plating solution through, and completely `filling, -said cell, in a manner to submerge and Wash over the surface ofr said depression; inaintaining su'oatmospheric pressure in said cell; passing an electric current from said surface as anode, through said cell for a short time; immediately thereafter passing an electric current of slightly less than the minimum plating density to said surface as cathode,

for at least a short time; then increasing the current density to that required to yielda satisfac- V tory deposit of chromium.

6. Electrolytic method of filling defects in metallic surfaces, which comprises; mechanically forming in a metallic surface at the locationl of a defect, a depression having a width which is great relative to its depth; imparting to saiddepression a smooth, continuous uninterruptedielectrically conducting surface throughout. its entirei area; blocking out a restricted areaV of said surface including and immediately surrounding said depression; constituting the electrically conducting surface of said restricted larea one electrode in an electrolytic cell; providing in said cell an-4 other electrode having a form corresponding to that of said depression; fixing said other electrode in place adjacent to and over the deepest part of said depression in such position that the edges of said depression Will nowhere be relatively much nearer to said'other electrode than sf the'vdee'pest part of said'depression; ele,ctrolytically. prepar'ing the metallic surface in said restricted: area; for receiving adherent'r electrofplate; cthe're'affter electrolytically depositing metal fin said rdepression; Vand maintaining during'said electrodeposition a substantially Vcontinuous flow ofelectroi, platingsolution through said cell, submergingand washing over the surfaceof said depression. 1,3117. Electrolytic'method of closing openings inf i metallic surfaces, i which comprises: closir'ig rthe Vbottomof such' an opening; impartin'gtfthe closed opening the'lformof a depression having and a continuous uninterrupted electrically concutting out the defect'to form a depression whose least width is great Vin comparison to its depth; providing said depressionwith a smooth, continuous, uninterrupted electrically conducting surface throughout its extent; blocking out a restricted areaof said chromium plated surface, including and immediately surrounding said depression; fixing an electrode of a form corresponding to said depression in position over and nearest to the deepest part thereof; passing a stream of chromium plating solution through the space between said depression and said electrode in a manner to submerge and wash over the surfaces of said electrode and said depression; passing an electric current for a short time from the surface of said depression as anode through said streamzof chromium plating solution to said electrode; then reversing the direction of `flow of current and maintaining a current density on the surface of said depression as cathode which is slightly less than the minimum plating density, for at least a short time; and then increasing 'the current density to one which causes the deposition of chromium in said depression.

9.`Process of patching a hole which extends through a chromium plated surface to ferrous base metal, which comprises: polishing out a restricted area, including and immediately surrounding said hole, to form a depression having a depth which is smallin comparison with its least Width, and having a. smooth, continuous, uninterrupted, electrically conducting surface throughout its extent; `fixing anelectrode insuch relation 'to said depressionthat the distance Vfrom saidfelectrode is less to the center than to the edges of said depression; maintaining chromium plating solution between and in contact with said electrode and the` surface of said depression; passing an electric current, for a shorttime,

' through said solution'from the surface of said depression as anode, to said electrode; substantially immediately thereafter passing an electric Icurrent, for at least a short time, through said solution. from said electrode to the surface of I said'depression as cathode; maintaining ther current density on said cathode, duringvs'aid time, e minimumzplating at a 'value' somewhatbelow t density; then increasing the current ;'to' a J'density suiiicient-v to accomplish the miuln';

10. Electrolytic method'of closingjopeningsin metallic surfaces, which comprises:V mechanically 'imparting to an openingthe form of a depression, 7 i lmateverially greater in width 0 than indepth; fillingV anyjpart'of the opening Whichis deeper than i i said depression with electrically conducting mai' tinuous `uninterrupted electricallyr conducting surface throughout its area; constitutings'aid deposition. O f j'chro-f V74electrolytic "cell;' preparing said surfacez of'3the depression for 'receiving' an Vadherent`'e1ectrofi deposit; and'thereafter'electrolyticallydepositing metal in said depression.

11; Method of closing'openingswhich extend through the thickness of sheet metal-,?which comprises: forming a -depression` -with-'sidessloping fromv saidv opening tothe: level of the 'adjacent surface; filling the Vopen-ing in the bottom of said depression With-electricallyficonducting material; impartingtosaid-depressionv a-1continuous '--uninterrupted1 electrically conducting ksurface throughout -its extent; electrolytically filling said depressionV with-metal; forming a1 depression Ion ythe other side of-- said'sheetmtal opposite to' said electrolytically-filleddepressionlimparting' to said second depression a continuouselectrically conducting surface throughout its11extent; and

electrolyticallylfilling saidsecondd'epression with metal.

i v12; Method of; closing -op'enings'which-i extend through the thickness of sheet vmetal; to vrender said sheet 'substantially homogeneous-throughout -fiits thickness;r which comprises: Lforming a vdev2 '-pifessionwithif'sides sloping'from said-opening to: the 'level of :the-1' adjacentfi'surface;ffilling the opening intthe bottom' of-.'saiddepression'iwith electrically conducting f material; 'limparting to said depression Ja continuous uninterrupted elec- I' trically conducting surface throughout i-tsiextent;`4 30 -preparing said surface for receivin'g'an'adherent i electrodeposit; Jelectrolyticall'y `fillin'g :said :depression with metal; forming; on the other side of said sheet metal, a depression of such depth as to completely remove: the filling material placed 35 in said 'original opening; 'imparting to said 'second r"depression a'continuouselectrically conducting surfacerv formed partly of-fthe' metal' electrodeposited in said first depression' preparing said surface for receiving anfadherent electrodeposit;

4, to rsaid depression a continuous uninterrupted -electrieally conducting surface-throughout its extent; blocking out a restricted area ofthesur- ...face including and immediately surrounding said depression; constituting the electrically conducting surface' of 'said' restricted area one electrode in an electrolytic`cell; preparing the surface of f -vthe metal in said restricted varea for-v receiving- =-an adherent electrodeposi't; electroly'ti'cally'filling said depression'vvith metal; forming a depression surrounding said hole on the opposite sideof the sheet; imparting to said -secondde- 'ipressionga 4continuous'electrically conducting surface: throughout itsfextenl'f;` blocking'zout a restricted area of the surface including and immediately surrounding said second depression; constituting the electrically conducting surface of said restricted area one electrode in an elec- 55 trolytic cell; preparing the surface of the metal in said restricted area for receiving an adherent electrodeposit; and electrolytically filling said second depression with metal.

f 14. Method of welding together edges of sheet metal, which comprises: holding the edges to be joined in the relative positions they are to occupy after welding; forming a depression with sides sloping from said edges to the level of the adjacent surface; filling the opening between said edges; at i the bottom i' of--- saidfl depressioniiwfith electrically'loonductingifiiaterial-limpartingi to f saididepression-fafcontinuous uninterr'uptedfelec- 1 trically conducting surface throughout it's f'ex't'ent; 5V -felectrolyticallyf-filling isaidf1`1epressior11'- Withiw'eld B''fmetal-g"foi'uning-a depression onfthefflother'side of saidsheet rrletal;l i opposite to Vsaid electrolytically filled depression imparting to' saldi-second depression a continuous 'ele'ctrcally'conducting -sur- -face throughout its :extentf f andifele'ctrolvti'cally "ffilling'said depression'with vveldmetal. '-1

edges of sheet metalfivh-ichi-comprises:holding f f the' k edges to be ijoined i'n'ijthefrelativeepositions i they are to occupy after V''fiweldin'g'; forming a'V de- '-the level ofthe'adjacent'surfaceffillingLthe'open- I ing 'between said edges? at-the bottom' of lsaid v"depression with-'1V electrically icnductingi 'mate- "'rialy im'parting to Isaidl'depression a lcontinuous 'uninterrupted i' electrically conducting isur'face throughout its'` extent; =eleotrolytically preparing 'said'surface to-'receive*-anfiadherent electrodeposit7"`-electrolytically`filling Vsaid depressioni `With "vveld metal; forming; on'the -other 'side ofi-is'aid `sheet'metaLopposite to said electrolyticallirlfilled `'depression'a depression o-fj'such' depth' as toom- 'pletely'rem'ove the rfilling-material-pla`ced in` 4said original "openingf impartng to `said V'second' depression' a' continuous electrically'eonducting sur- 'face' throughoutitsV extent f' said -surface|`` being formed' partly ofthefmetali'elect'odeposited' in 'said' first vdepression?` jelectrolytically1'pi'eparing Y 'said surface to''-'re`ceiveI an; -fiadherient electrode- 'posit and 'eleetrolyticallyi filling said rsecond'gdepression with Weldm'tal; I

` 161 Electrolytic" method" of closing'lfopenings i vvhiclrr'A extend through 'the thicknessr off-sheet metal; vvhich4 A:comprises r'l prep'a'ring; orfi'onefside 40" of 'sai'd'sheet 'metaL'a surface of Llinv'iit'ed'iareaz suri' "rounding' the' 'opening to be closed; said preparai tionv 'including' the 'filling of 'said' openinglffiush with the prepared' surface,` with'electrifca'lly''r cond'u'c'ting-'m'aterial;'A to' render the l-''surfacevin said flirn'ited 'area' smooth, V:continuous;Jandlelectrically 'i conducting'across said opening; 2'said preparation further 'including `a'*treatment" tol-conditioni'ithe 'f Tmetal of' said'sheet in' said'limitedfareaj'for the reception 'of a"'meta'llic" ele'ctrod-eposit;selectro-v depositing af material'thickness' of -metaljon1 said area mechanically"removing f said "elgectrically conducting. filling' 'material together 'With fadjai :cent metalK of' the 'sheet by: cutting v'from`v the 'opj'posite'side of said sheet metal tofformjadepression m' the 'surface of; said. opposite :sida-said depression' extending'ithroughf the-metal'of 'the f sheet 'into the afores'aid' 'electrolyticallvjdeposited metal; preparing the' surface of 'saidi 'depression 60, -forthe receptionf 'of an La'dherent `elec'tifo'deposit; Ur-j-and gelectrolyticallf'filling 'said 'depression' with metal.

17. Electrolytic method of welding together abutted edges of sheet metal parts, which comwelding; preparing, on one side of said sheet metal, a surface of limited areav extending in both directions from the -line of abutment, said tween the abutted edges flush with the prepared surface, with electrically conducting material, to render the surface in said limited area smooth, continuous, and electrically conducting across the line of abutment, said preparation further prises: temporarily holding said abutted edges in Y the relative positions they are to occupy after preparation including the filling of the space be-v including a treatment p said sheetmetalparts in said limited area; for

te eonditien the metei er the reception'of a metallic electrodeposit; ;electrodepositing amaterial thickness of metal on said area; mechanically removing said electricallyV conducting vfilling materialtogether with adjacent metalV of .the sheetfby cutting a depression 'extending fromV the opposite sidethrough the metal of said sheet'qinto the aforesaidelectroi lytically deposited metal; preparing the surfacel of said depression for the-reception ofv an adherent electrodeposit; andelectrolytically filling said depression with metal.

18'.l Methodof Securing an adherent electrovdeposit ofchromium on at'least a part of the surface of a metallic body, which surface is composedof at least` one metal chosen from the class consisting Vof iron and chromium, which com- V ;surfac-e of a metallic-'bodyrwhich part of said surface islcomposed' of atleast one of' the metals chosen fromvthe class cqnsi'sting of iron and chromium, which comprises subjecting the metal composing said part of said surfacetoia'treat- I ment -consisting of the following steps: ashort anodic treatment in the chromium plating solution; follovsgVedv-by -a cathodic treatment of at least a Ifew's-econds duration, in said chromium plating solution, at a currentdensity insuificient to depositany chromium'on the cathode; foll lowed byja cathodic treatment at a current density sufiicient'to cause, the desired deposition of 1 chromium thereon; said cathodic-treatment at less than plating density being initlated vbefore any applicationV of plating density current and prises a treatment consisting of Vthe following steps: submerging the part of said surface on which the electrodeposit is to be made, in a chromium plating solution; anodically treating said part of said surface by passing an electric current through said solution from said surface as anode for ashort time; followingthis by a cathodic treatment which is accomplished by passing an electric current of somewhat less' than plating density through saidv solution for at least .a -few seconds before any application of plating density current, to improve the adherencethereto of thechromium subsequentlytdeposited thereon; thenfwhile maintaining the flow of current to said part of said surface as cathode, increasing i the current densityfto adensity at which elec- V trodeposition of chromium occurs on the cathode, to initiate depositionfthereoft' 19. Methodof securing an adherent electroshort'time; thereafter, and prior to any application of plating density current thereto, cathodii cally treating said metaL'n a chromium plating solution, for at least a few seconds, to improve the adherence thereto'ofthe chromium subscvquentlyv deposited thereon; then'jpassing a plating'current to said metal as cathode to form the desireddeposit thereon; saidlcathodic treatment being carried out' at a cathode current density somewhat'less than the minimum value at which :chromium will'be deposited from 'said'platlng solution, 'and being continued until' the platlng deposit of chromium 'on at least Va part of the (surface ofk a metallic body,'`wliich part of said surface is composed o'fatfleast one of the metals chosen from the class consisting V of iron and chromium, which comprises subjecting the metal Composing saidpart of said surface to 'agtreatment consistingf of 'thefollowing steps: anodically treating said lmetal in 'a chromium plating solution, fora short time;fthereafter, 'and prior to anyV application of plating densitycurrent thereto, cathodically fitreating said metal, in a chromium. plating'r solution; for 'at' least a few seconds, to improve the adherence ther-etc of the chromium. subsequently deposited' thereon cathode to form the desired deposit thereon; said cathodic treatment being carried out at a cathfrom said plating s'oluti on,` and'being continued 20. Methodpfsecuring an adherent velectro-V 'fiimmberf sol V., then, passing a plating current to said metalV as until the plating current is applied'and the depolstion'of chromiu'minitiated. i V

deposit Vof chromium on at least 'a 'partiof'the current isappli'edf and the depositiontof chroinitiated. v i

' P1111111? s. iailioKNsDERFER;

REFERENCES cITEn H lThe followingv references are of record in the file of this'patentzt-V` 'UNITED VSTATE'S PATENTS Date :Name 1,09 0, 456 Darrah Mar. 17,1914' l,285,87.5 I Woodbury Nov. 26,' 1918 1,'645,9,27 Pierce Oct. .18, 1927 1,757,67l i Langseth 'May 6, 1930 1,809372 Sderberg June 16, 1931 1,909,71'6 Pinner May 16, 1933 i 1,918,60 5 Jones July 18,'1933 aocsfis'o Vsem11em Dee. a, 1936 412593319 p Domm Augfze, 1942 Y i EOREIGN VPATENis `Number. l` VCountry f i `Date i 154,282,r Great Britain f iNoy. 8,1920 Great Britain'. ;Apr.- 23,'1920 

1. ELECTROLYTIC METHOD OF CLOSING OPENINGS IN METALLIC SURFACES, WHICH COMPRISES: MECHANICALLY IMPARTING TO AN OPENING THE FORM OF A DEPRESSION WHOSE DEPTH IS SLIGHT RELATIVE TO ITS LEAST WIDTH; FILLING ANY PART OF THE OPENING WHICH IS DEEPER THAN SAID DEPRESSION, WITH ELECTRICALLY CONDUCTING MATERIAL; PROVIDING SAID DEPRESSION WITH A CONTINUOUS UNINTERRUPTED ELECTRICALLY CONDUCTING SURFACE THROUGHOUT ITS ENTIRE AREA; ENCLOSING THE ELECTRICALLY CONDUCTING SURFACE OF SAID DEPRESSION IN AN ELECTROLYTIC CELL; ELECTROPYTICALLY PREPARING THE SURFACE OF SAID DEPRESSION FOR RECEIVING AN ADHERENT ELECTROPLATE; THEREAFER ELECTROLYTICALLY DEPOSITING METAL IN SAID DEPRESSION, AND MAINTAINING DURING SAID ELECTRODEPOSITION A SUBSTANTIALLY CONTINUOUS FLOW OF THE ELECTROPLATING SOLUTION THROUGH SAID CELL, SUBMERGING AND WASHING OVER THE SURFACE OF SAID DEPRESSION. 